The long-term objectives of this work are to develop experimental techniques which, by significant improvement of the detection sensitivity of nuclear quadrupole resonance (NQR) transitions, will enable routine NQR study of large molecules, e.g., biologically significant ones. Specifically, this project is a study of how double-irradiation schemes can accomplish these aims. It is proposed to study the response of NQR systems to non-resonant audio frequency irradiation and to take advantage of these techniques to increase the effective sensitivity of multiple- pulse NQR spectroscopy. So far, results have been obtained in half- integer spin systems and for axially symmetric integer-spin systems. In both cases, we have observed a significant increase in spin-spin relaxation time. Two distinct benefits have accrued from this "line narrowing" (i) sensitivity has been enhanced due to the lengthening of echo-train decay, and (ii) resolution of underlying fine-structure was increased. In continuing this work, it is proposed to adapt field- dressing theory to perturbations of integer-spin NQR systems for axially and non-axially symmetric electric field gradients, and to extend experimental observations to the latter case, which is vastly more common. This work involves both theoretical and experimental efforts. For the latter, a special double irradiation sample head has been constructed to enable variation of the polarization of the audio- frequency field. The NQR multiple-pulse techniques involved have been developed by the author. The impact of this work on NIH related goals will be to provide students with far-above-average exposure to instrumentation and to the fundamentals of magnetic resonance theory and experiments. Furthermore, sensitivity improvement may enable more precise structure and bonding studies of biomolecules by adding a high resolution spectroscopic techniques to the magnetic resonance repertoire available to biochemists and biophysicists.